1. Field of the Invention
This invention relates in general to quantum computation, and in particular to quantum computation with quantum dots and terahertz cavity quantum electrodynamics.
2. Description of Related Art
A quantum computer processes quantum information which is stored in “quantum bits,” also called qubits. If a small set of fundamental operations, or universal quantum logic gates, can be performed on the qubits, then a quantum computer can be programmed to solve an arbitrary problem. Quantum computation has been shown to efficiently factorize large integers, and the quantum information can be stored indefinitely, which provides the interest in quantum computation and machines that can perform quantum computation.
Consider, for example, the publication by Barenco, et al., entitled “Conditional Quantum Dynamics In Logic Gates,” Physical Review Letters, 15 May 1995, USA, vol. 74, no. 20, pages 4083–4086. This publication notes that quantum logic gates provide fundamental examples of conditional quantum dynamics, and could form the building blocks of general quantum information processing systems, which have recently been shown to have many interesting non-classical properties. This publication describes a simple quantum logic gate, the quantum controlled-NOT (CNOT), and analyzes some of its applications. The publication also discusses two possible physical realizations of the gates, one based on Ramsey atomic interferometry, and the other on the selective driving of optical resonances of two subsystems undergoing a dipole—dipole interaction.
However, the implementation of a large-scale quantum computer has remained a technological challenge. The qubits must be well isolated from the influence of the environment, but must remain manipulatable in individual units to initialize the computer, perform quantum logic operations, and measure the result of the computation.
Implementations of such a quantum computer have been proposed using atomic beams, trapped atoms and/or ions, bulk nuclear magnetic resonance, nanostructured semiconductors, and Josephson junctions. However, each scheme proposed has limitations that make large-scale implementation difficult and very limiting in performance.
For example, proposals using trapped atoms or ions, qubits couple with collective excitations or cavity photons. This coupling enables two-bit gates involving an arbitrary pair of qubits which makes programming straightforward. However, these schemes require serial gating schemes, whereas error correction schemes require parallelism, thereby limiting the usefulness of data gathered using an atomic or ion trapping machine.
In the semiconductor and superconductor schemes, only nearest-neighbor qubits can be coupled, and significant overhead is required to couple distant qubits. However, these machines can perform some gate operations in parallel, which allows for some error correction.
It can be seen, then, that there is a need in the art for a quantum computer. It can also be seen, then, that there is a need in the art for a quantum computer that can perform parallel gate operations. It can also be seen, then, that there is a need in the art for a quantum computer that can perform parallel gate operations without significant qubit overhead.